1. Field of the Invention
The present invention relates to a spindle motor control system for controlling a spindle motor rotating an optical disk at a constant linear velocity for a disk player of an optical recording and/or reproducing apparatus, maintaining a data-reproducible rotation of a spindle motor even when reproduction data for controlling a constant linear velocity in rotating an optical disk is not obtained due to an off-track condition, noise or the like.
2. Description of the Prior Art
In a conventional optical recording/reproducing apparatus using an optical disk, various kinds of disks are widely used in a disk player, for example, a compact disk (CD), mini disk (MD) and the like, having a spiral recording track or concentric tracks formed thereon. In operating the disk player, in order to maintain a constant linear velocity (referred to as "CLV", hereinafter) in rotating an optical disk during a recording/reproducing operation, there has been employed a spindle motor servo-control system in the disk player for servo-controlling a spindle motor to obtain a rotation of the optical disk having a constant linear velocity (CLV), where the CLV control is performed based on rotational speed or angular velocity data of clock components extracted from periodic tracking servo digital data having a given period which the periodic data was previously recorded at a constant linear velocity along on a recording track or tracks formed on the optical disk.
The following briefly describes a general data format recorded on an optical disk in the case of using, for example, a compact disk having a spiral track along which periodic digital data is previously recorded in a CLV mode. This recorded digital data has durations each defined by a first transition and last transition from a leading edge to a trailing edge or vice versa, which each of the durations is limited to a predetermined range of, e.g., 3T to 11T assuming that T is a given reference period of, e.g., about 231 nano-sec (i.e., 4.3218 MHz) as shown in FIG. 10A. Also, two pieces of the longest data having the maximum duration of 11T are continually recorded in accordance with a frame sync signal having a given frequency of e.g. 44.1 kHz. Accordingly, when the digital data is reproduced, the leading and trailing edges are detected to calculate the longest period as shown in FIG. 10B. Thus, the spindle motor is controlled to have a rotational speed or angular velocity so that the calculated longest period corresponds to the maximum duration of 11T (=nearly 2.55 .mu.sec in this case), thereby obtaining a CLV control of the spindle motor.
FIG. 9 shows an example of a conventional servo-control system for controlling a drive of a spindle motor used in an optical disk player.
In FIG. 9, reference numeral 1 denotes an optical disk having periodic digital data recorded, which the recorded data including tracking servo digital data is reproduced through an optical head 2, and the reproduced data is amplified by an RF amplifier 3 which serves as a waveform rectifying means. The RF amplifier 3 rectifies the reproduced data in waveform to be suitable for digital signal processing by slicing the waveform at a predetermined slice level having a given duty rate as shown in FIG. 11A.
Reference numeral 4 denotes a focus/tracking control unit for obtaining focus and tracking conditions of a light is beam spot applied from the optical head 2 onto the optical disk. Reference numeral 5 denotes a clock extracting unit which serves as e.g. a longest period calculating means for obtaining a CLV of the optical disk by extracting a clock signal component from the waveform-rectified reproduction data outputted from the RF amplifier 3 as shown in FIG. 11B.
When the focus and tracking servo-controls are both normally effected, the longest period calculated in accordance with the extracted clock component is proportional to the rotational speed of the spindle motor and then the output of the clock extracting unit 5 is fed to a CLV control unit 6 which controls a spindle motor 8 in accordance with the extracted clock component, by generating a motor drive signal so that the data of the longest period is coincident with the given longest period (11T in the above case) with reference to a reference clock generated by a reference clock generator (not shown). Thus, the drive signal outputted from the CLV control unit 6 is applied to the spindle motor via a loop filter (not shown) and a driver (not shown), so that the spindle motor 8 is driven in accordance with the drive signal to thereby rotate the optical disk under a CLV control mode.
Whereas, when a light spot from the optical head is in an off-track condition due to such as undesirable external shock or vibration, the slice level can not follow the variation in DC component of the applied signal in the RF amplifier 3, resulting in causing burst in rotation of the spindle motor.
In order to avoid this undesirable rotation, an off-track detection unit 13 is provided in parallel to the clock extracting unit 5 so that a switch 14 is switched off to cut off the transmission of the spindle motor drive signal in a CLV servo-control loop. In more detail, the off-track detection unit 13 receives the output of the RF amplifier 3 to detect the off-track condition of the light spot, and the output of the off-track detection unit 13 is applied to a control input terminal of the switch 14 so that the switch 14 is switched on/off of the transmission of the drive signal outputted from the CLV control unit 6 to the spindle motor 8, in accordance with the detection result detected by the off-track detection unit 13 as shown in FIGS. 11C and 11D.
By this conventional arrangement, when the light spot applied from the optical head 2 is in a state of an off-track condition on the optical disk 1, the off-track condition is detected by the off-track detection unit 13, and the switch 14 is then switched off based on the detection result outputted from the off-track detection unit 13 to thereby cut off the transmission of the drive signal outputted from the CLV control unit 6 to the spindle motor 8 so that the spindle motor is rotated only by its inertia, thereby preventing the burst rotation of the spindle motor.
In this conventional arrangement, however, when the reproduction data per se is not obtained in the recording/reproducing operation due to cracks and stains on the optical disk or due to external shock or vibrations applied from the outside, the clock signal component can not be extracted and the CLV control can not be effected, resulting in causing undesirable burst rotation of the optical disk in some cases.
Moreover, in the optical disk player, it is essentially required to maintain a rotational speed or angular velocity of the spindle motor sufficient to effect a recording/reproducing operation in stable during the operation. In view of this requirement, however, there has been further involved a problem in the conventional system such that the CLV control in rotation of the optical disk can not be maintained because the CLV servo-control loop is switched off.